Method and apparatus for operating an electrical switch in a moisture-laden environment

ABSTRACT

An electrical switch for operation in a moisture-laden environment has an operating shaft extending outwardly from a housing therefor through an elastic sleeve of insulating material. The elastic sleeve has an initial diameter less than the diameter of the shaft and is telescoped over the latter in dilated condition so as to form an interference fit with the shaft to accommodate any surface defects and eccentricity in the latter and provide a moisture seal. An insulating jacket is cast around the sleeve as well as the switch housing, thus assuring the formation of a fluidtight seal while providing support for the operating shaft and sleeve.

United States Patent Inventor James T. Odom Centralia, Mo.

Appl. No. 853,438

Filed Aug.'27, 1969 Patented Aug. 31, 1971 Assignee A. B. Chance Company Centralia, Mo.

METHOD AND APPARATUS FOR OPERATING AN ELECTRICAL SWITCH IN A MOISTURE-LADEN ENVIRONMENT [56] References Cited 7 UNITED STATES PATENTS 3,287,535 11/1966 Bauer 200/168 G 3,373,257 3/1968 Matthiaset al. 200/168 G X 3,471,669 10/1969 Curtis 200/168 G Primary Examiner -l-l. 0. Jones Att0rneySchmidt, Johnson, Hovey & Williams ABSTRACT: An electrical switch for operation in a moistureladen environment has an operating shaft extending outwardly from a housing therefor through an elastic sleeve of insulating material. The elastic sleeve has an initial diameter less than l2 Chins, 4 Drawing Figs.

US. Cl. 200/168 G, 264/272 Int. Cl H0lh 9/04 Field ofSeareh 200/168 G; 174/18, 37; 264/272 METHOD AND APPARATUS FOR OPERATING AN ELECTRICAL SWITCH IN A MOISTURE-LADEN ENVIRONMENT This invention relates to electrical switching apparatus and, more particularly, to a method and apparatus for operating an electrical switch in a moisture-laden environment.

It has been the practice, in recent years, to locate much of the electrical distribution equipment in residential areas underground to avoid the cluttered appearance that results when this equipment is located above ground. An underground switch assembly of the type to which the present invention is particularly directed is described in detail in U.S. Pat. No. 3,471,669, the same being incorporated herein by reference to the extent necessary to obtain a full and complete understanding of the present invention. Vacuum interrupter switching units of the type described in the aforementioned patent are uniquely suited for underground use because of their low maintenance requirements and the sealed compact construction which allows the unit to be enclosed by a solid in.- sulation material. When the insulated unit is located in a very moist atmosphere or an area where it may be completely submerged in a conducting liquid such as water, it is essential that the insulating material be completely sealed against the penetration of any moisture that would degrade its insulative properties. This is a particular problem when it is necessary to have external means of mechanical operation of the switch, requiring that the insulating material be penetrated by a suitable shaft or handle. Such shaft or handle must be free to rotate, or move in a longitudinal direction, yet moisture penetration along the shaft must not be permitted if the integrity of the insulation system is to be maintained.

It is, therefore, the primary objectof this invention to provide a method and apparatus for external mechanical operation of an encapsulated electrical switch which will maintain the integrity of the insulation system when the switch is completely submerged in a conductive liquid such as water.

It is also an object of this invention to provide a method and apparatus as aforesaid where the external operating means is provided with a fluidtight seal having low resistance to actuation of the sealed operating component.

Furthermore, it is an important object of this invention to provide a method and apparatus for external mechanical operation of an electrical switch in a moisture-laden environment wherein an elastic sleeve of insulating material is telescoped over an operating shaft to form an interference fit with the latter and wherein the resiliency ofthe sleeve accommodates surface defects and eccentricity in the shaft to prevent the entrance of moisture into the switch which, if permitted, would cause a failure of the insulation system.

As a corollary to the above object, it is another aim of this invention to provide an elastic sleeve of insulating material having an initial diameter less than the diameter of the operating shaft, which sleeve is telescoped over the operating shaft in dilated condition to form a fluidtight seal therewith.

Still another object of this invention is to provide a method and apparatus as aforesaid wherein an easily accessible operating arm for the operating shaft is provided, which arm is a sealed part of the encapsulated unit.

Additionally, a very important object of this invention is to provide a method and apparatus for operating an electrical switch encapsulated in an insulating material wherein a fluidtight seal for an operating shaft is formed by an elastic sleeve and wherein the elastic sleeve is configured to present a stress cone at one end thereof to relieve electrical stresses along the sleeve-shaft interface.

Yet another object of this invention is to provide a method of rendering an electrical switch operable in a moisture laden environment wherein the insulating material for the switch is cast around the operating shaft as well as the switch housing, thus assuring the formation of a fluidtight seal while also providing support for the operating shaft.

Other objects of the invention will be made clear or will become apparent from the following description.

In the drawing:

FIG. I is a perspective view of an encapsulated electrical switch having extemal'operating means;

FIG. 2 is an enlarged, fragmentary, cross-sectional view of the switching apparatus shown in FIG. 1 taken along the central longitudinal axis of the operating shaft, certain portions being shown in elevation to reveal details of construction;

FIG. 3 is a view similar to FIG. 2 showing an alternative form of the invention; and

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2.

Referring initially to the embodiment illustrated in FIG. I and shown in detail in FIG. 2, an encapsulated switching apparatus is designated generally by the numeral 10 in FIG. 1 and includes a moisture barrier for the switch (not shown) such as a housing 12 (partially visible in FIG. 2), and a layer of insulating material 14 around the housing 12. A pair of frustoconical sheaths l6 and 18 surround the respective female connectors of the apparatus 10. A thin layer of metal 20 along the outer periphery of the insulative material 14 provides elecu'ical shielding of the apparatus 10, and a layer of asphaltic paint 22 protects the metal layer 20 from corrosion. An annular band 21 around the central body portion of the apparatus l0 normally includes a suitable clamp (not shown) for securing the apparatus to an appropriate support such as that usually found in an underground distribution vault.

External operating mechanism for the apparatus 10 extends through an opening 24 in the housing 12 and includes a hearing 26, a retaining ring 28, and a collar 30 through which an elongated, rotatable operating shaft 32 of fiberglass-reinforced epoxy synthetic resin or other insulative material passes. As indicated by the broken lines in, FIG. 2, in addition to extending outwardly from the opening 24, the shaft 32 also extends within the housing 12. It is to be understood of course, that the shaft 32 is jointed to appropriate operating mechanism within the housing 12 in a conventional manner so as to permit operation of the switch by rotation of the shaft 32. Suitable operating mechanism is shown and described in detail in the above-referenced U.S. Patent.c8 An L-shaped operating arm 34 having an end bore only slightly larger than the outside diameter of the shaft 32 is telescoped over the externally extending end of the latter and secured thereto by an appropriate adhesive, cross pin or other suitable means.

An elongated, cylindrical elastic sleeve 36 which is preferably formed from an elastomeric material such as Nordel rubber, an ethylene propylene diene (modified) polymer sold by E. l. du Pont de Nemours & Co., of Wilmington, Delaware, but may also be formed from other synthetic rubbers, as well as natural rubber, surrounds the shaft 32 in an interference fit therewith as clearly shown in FIG. 4. A cup shaped collar 38 formed from a conductive material, which may be a resinous material filled with carbon black, is disposed intermediate the housing 12 and the inner end of the sleeve 36 and receives the bearing 26. The outer face of the cup-shaped collar 38 abuts the inner end of the sleeve 36 and is secured to the latter by a suitable adhesive. The rim of the collar 38 engages the housing 12 and a head 40 of silicone rubber or other appropriate sealant forms a fluidtight seal between the collar 38 and the housing 12.

An O-ring gland 42 is disposed in abutting relationship to the sleeve 36 at the outer end of the latter and has an inner bore of slightly larger diameter than the shaft 32. The inner bore is internally grooved to receive an O-ring 44. A second, outer bore of larger diameter than the inner bore and concentric with the latter, similarly receives a pair of O-rings 46 and 47 which form a bearing for the operating arm 34. In some instances it is desirable to place a layer of insulating lubricant along the sleeve-shaft interface to facilitate rotation of the shaft 32. It will be seen from FIG. 1 that a conductive line 49 connects the operating arm 34 with the support band 21 for grounding purposes.

In operation, movement of the operating arm 34 rotates the shaft 32 to effect the switching operation. The disposition of the O-rings 44, 46 and 47, together with the interference fit between the sleeve 36 and the shaft 32, prevents the entrance of moisture into the apparatus through the opening 24. It is to be understood that the sleeve 36 is of a smaller initial inside diameter than the outside diameter of the shaft 32 and is telescoped over the latter in dilated condition. This assures that the sleeve 36 accommodates any surface defects or eccentricities in the shaft 32 and forms a fluidtight seal. The conductive collar 38 which is disposed in surrounding relationship to the shaft 32 and at least the outboard portion of the bearing 26, serves to relieve electrical stresses emanating from the bearing 26 and the part of the housing 12 adjacent the opening 24.

It is preferred that at least three O-rings 44, 46 and 47 be disposed within the gland 42 for proper sealing of the operating arm 34 and the outer end of the shaft 32. Since, in assembly, the collar 38 and the sleeve 36 are telescoped over the shaft 32, the gland 42 is positioned in abutting relationship to the sleeve, the operating arm 34 is positioned in the gland 42, and the insulating material 14 then cast around the aforementioned assembled components, the O-ring 44 prevents any of the material 14 from passing between sleeve 36 and the gland 42 from flowing outwardly along the shaft 32. The Oring 47 performs the same function with regard to any of the material 14 entering the open end of the gland 42. This leaves the central O-ring 46 free of any insulation material 14 which, upon solidification, could interfere with the formation of a fiuidtight seal with the contacting surface of the arm 34. The insulating material 14 is preferably an epoxy resin which, upon solidification, is relatively rigid and of a substantially greater degree of hardness than the sleeve 36. The material 14 thus serves to maintain the sleeve 36 in tight sealing engagement with the shaft 32 when the latter is rotated.

In the embodiment shown in FIG. 3, an elastic sleeve 48 is formed to present a generally frustoconical end portion 50 that engages a complementally configured conductive stress cone 52, the latter being desirable when the operating voltages are sufficiently high. The ring 52 may be metallic or a filled conductive resin (as illustrated), and is provided with an annular flange portion surrounding the bearing 26 and engaging the housing 12. Other features of the apparatus illustrated in FIG. 3, including the assembly and operation thereof, are identical with those previously described for the apparatus shown in detail in FIG. 2. It will be appreciated that in both embodiments of the invention it is advantageous to cast the insulation material 14 around the housing 12 simultaneously with the casting thereof around the sleeve 36 and the gland 42. This assures the formation of a fluidtight seal around the housing and, upon solidification, the material 14 provides support for the operating shaft 32. It is, of course, apparent that construction of the apparatus 10 so as to prevent the entrance of a conducting liquid thereinto when completely submerged, also serves to maintain the integrity of the insulation system in a moistureladen environment such as is commonly present in underground vaults even though the apparatus is not completely submerged.

From the foregoing description it is also apparent that the present invention contemplates a method of rendering an electrical switching unit operable in a moisture-laden environment. The unit is encapsulated within a moisture barrier having an opening therein from which the operating shaft of the unit extends. An elastic sleeve is telescoped over the shaft and has an initial diameter less than the diameter of the shaft, the sleeve thereby being in dilated condition to provide a moisture seal while also permitting the necessary movement of the shaft incident to switch operation. A moisture seal is provided between the inner end of the sleeve and the barrier, and a bearing is positioned over the shaft adjacent the outer end of the sleeve. An operating element, such as the projecting leg of the L-shaped arm 34, is disposed within the bearing and forms a seal therewith. As a final step, an insulating jacket is cast around both the moisture barrier and the sleeve in supporting relationship to the latter.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. Apparatus for operating an electrical switch in a moisture-laden environment comprising:

a moisture barrier for the switch having an opening therein;

switch-operating mechanism passing through said opening and including a movable operating shaft extending therefrom;

cover means surrounding said shaft and disposed in sealing relationship to said barrier, and provided with an elastic sleeve having an initial diameter less than the diameter of said shaft,

said sleeve being telescoped over said shaft in dilated condition to effect a moisture seal therewith and for movement of the shaft within the sleeve, whereby to prevent the passage of moisture through said opening past the barrier while permitting operation of the switch; and

an insulating material disposed around said sleeve in supporting relationship thereto.

2. Apparatus as claimed in claim 1, wherein said insulating material is relatively rigid and of a substantially greater degree of hardness than said sleeve for maintaining the latter in tightsealing engagement with said shaft.

3. Apparatus as claimed in claim 1, wherein is provided bearing structure carried by the barrier within said opening therethrough and rotatably supporting said shaft, and said cover means includes an annular conductive member in surrounding relationship to said shaft and at least the outboard portion of said bearing structure for confining electrical stress emanating from said bearing structure and the adjacent part of said barrier.

4. Apparatus as claimed in claims 3, wherein said annular member is of generally conical configuration.

5. Apparatus as claimed in claim 3, wherein said annular member is of cup-shaped configuration.

6. Apparatus as claimed in claim 1, said insulating material extending outwardly beyond said sleeve, there being bearing means adjacent said sleeve at its outer end and supported by said material, said bearing means including sealing means engaging the shaft for preventing passage of fluid between the shaft and the bearing means.

7. Apparatus as claimed in claim 6, wherein is provided an operating arm on said shaft and disposed within said bearing means, said sealing means including at least one sealing component in sealing engagement with said shaft, at least one sealing component in sealing engagement with said operating arm, and at least one shaft engaging sealing component intermediate the first two sealing components.

8. A method of constructing electrical switching apparatus which is operable in a moisture-laden environment, wherein said apparatus includes a switching unit and a movable operating shaft extending from the unit, said method comprising the steps of:

providing a moisture barrier for said unit having an opening therein from which said shaft extends;

telescoping over said shaft an elastic sleeve having an initial diameter less than the diameter of the shaft;

effecting a moisture seal between the sleeve and the barrier;

and Y placing an insulating jacket around said sleeve in supporting relationship thereto.

9. A method as claimed in claim 8, wherein the step of placing said jacket around the sleeve includes casing a jacket therearound of greater hardness than said sleeve.

10. A method as claimed in claim 8, wherein the step of providing a moisture barrier for the unit includes encapsulating said unit within said moisture barrier.

11. A method as claimed in claim 10, wherein the step of placing said jacket around the sleeve includes casting the jacket around the barrier and the sleeve.

12.'A method as claimed in claim 8, wherein is included, prior to the step of placing said jacket around said sleeve, the steps of positioning a bearing over said shaft adjacent the end of said sleeve remote from said barrier; and disposing an operating arm for said shaft within the bearing, the step of placing said jacket around the sleeve including surrounding said bearing with said jacket to support the bearing. 

1. Apparatus for operating an electrical switch in a moistureladen environment comprising: a moisture barrier for the switch having an opening therein; switch-operating mechanism passing through said opening and including a movable operating shaft extending therefrom; cover means surrounding said shaft and disposed in sealing relationship to said barrier, and provided with an elastic sleeve having an initial diameter less than the diameter of said shaft, said sleeve being telescoped over said shaft in dilated condition to effect a moisture seal therewith and for movement of the shaft within the sleeve, whereby to prevent the passage of moisture through said opening past the barrier while permitting operation of the switch; and an insulating material disposed around said sleeve in supporting relationship thereto.
 2. Apparatus as claimed in claim 1, wherein said insulating material is relatively rigid and of a substantially greater degree of hardness than said sleeve for maintaining the latter in tight-sealing engagement with said shaft.
 3. Apparatus as claimed in claim 1, wherein is provided bearing structure carried by the barrier within said opening therethrough and rotatably supporting said shaft, and said cover means includes an annular conductive member in surrounding relationship to said shaft and at least the outboard portion of said bearing structure for confining electrical stress emanating from said bearing structure and the adjacent part of said barrier.
 4. Apparatus as claimed in claims 3, wherein said annular member is of generally conical configuration.
 5. Apparatus as claimed in claim 3, wherein said annular member is of cup-shaped configuration.
 6. Apparatus as claimed in claim 1, said insulating material extending outwardly beyond said sleeve, there being bearing means adjacent said sleeve at its outer end and supported by said material, said bearing means including sealiNg means engaging the shaft for preventing passage of fluid between the shaft and the bearing means.
 7. Apparatus as claimed in claim 6, wherein is provided an operating arm on said shaft and disposed within said bearing means, said sealing means including at least one sealing component in sealing engagement with said shaft, at least one sealing component in sealing engagement with said operating arm, and at least one shaft engaging sealing component intermediate the first two sealing components.
 8. A method of constructing electrical switching apparatus which is operable in a moisture-laden environment, wherein said apparatus includes a switching unit and a movable operating shaft extending from the unit, said method comprising the steps of: providing a moisture barrier for said unit having an opening therein from which said shaft extends; telescoping over said shaft an elastic sleeve having an initial diameter less than the diameter of the shaft; effecting a moisture seal between the sleeve and the barrier; and placing an insulating jacket around said sleeve in supporting relationship thereto.
 9. A method as claimed in claim 8, wherein the step of placing said jacket around the sleeve includes casing a jacket therearound of greater hardness than said sleeve.
 10. A method as claimed in claim 8, wherein the step of providing a moisture barrier for the unit includes encapsulating said unit within said moisture barrier.
 11. A method as claimed in claim 10, wherein the step of placing said jacket around the sleeve includes casting the jacket around the barrier and the sleeve.
 12. A method as claimed in claim 8, wherein is included, prior to the step of placing said jacket around said sleeve, the steps of positioning a bearing over said shaft adjacent the end of said sleeve remote from said barrier; and disposing an operating arm for said shaft within the bearing, the step of placing said jacket around the sleeve including surrounding said bearing with said jacket to support the bearing. 